Photoreceptors are the first stage in the visual process and therefore limit the information an animal can extract from its environment. The gain, noise and kinetics of phototransduction, along with the membrane properties of photoreceptor inner segments, determine the maximum performance of rods and cones in the mammalian visual system. This in turn sets the upper limit on overall visual system performance. The long-term goal of this project is to quantify the physiological mechanisms that underlie human visual sensitivity by studying the photovoltages recorded from photoreceptors in the macaque retina using a perforated patch technique. The first aim is to determine rod and cone detection thresholds as a function of background intensity and to determine the functional significance of rod/cone coupling. Photoreceptor thresholds will be directly compared to dark- adapted and light-adapted psychophysical thresholds. The second aim is to determine the temporal frequency characteristics of signal and noise in rods and cones and compare to human temporal sensitivity. The third aim is to determine the specificity of midget bipolar cells for cones of a particular spectral type and to determine the relationship between cone response properties and post-synaptic wiring. These investigations can provide further insights into the mechanisms that shape the photoreceptor component of the human ERG and can potentially lead to a greater understanding of the effects of disease on retinal sensitivity.